Process for the dealkylation of alkyl naphthalene



United States Patent 3,102,151 PRSCESS FGR THE DEALKYLATION OF ALKYL NAPHTHALENE Robert G. Haldeman, Ecuth Norwalk, and George Cas- The present invention relates to a process for the deaikylation of alkyl naphthalenes, and more particularly to the demethylation of methyl naphthalenes.

Petroleum methyl naphthalene fractions obtained from petroleum hydrocarbon fractions, or coal tar methyl naphthalene fractions, contain substantial portions of methyl naphthalenes, a relatively low cost, readily available material for which there is no important commercial utility.

Because of its availability and low cost, as for example, with respect to naphthalene, it would be highly desirable if the methyl naphthalene in such fractions could be converted to more useful products, such as for example, naphthalene, an important use of which is in the manufacture of phthalic anhydride.

Unfortunately, petroleum alky-l naphthalene fractions and coal tar alkyl naphthalenes frequently contain suba stantial amounts of sulfur, and if converted to naphthalene, to be employed in the preparation of phthalic anhyvdride, the sulfur present results in relatively rapidly declining yields of phthalic due to catalyst poisoning. Within limits, declining yield may be partially offset by increasing the temperature of reaction. As temperatures are increased further, yields decline, equipment life is shortened, as well as is the useful life of the catalyst.

Accordingly, it is an object of this invention to provide a process whereby heretofore undesirable and relativelyinexpensive alkyl naphthalene-containing fractions, and in particular methyl naphthalene-containing fractions,

whether they be petroleum or coal tar source fractions containing sulfur, are readily desulfurized and dealkylated to naphthalenes suitable for use as teed stock in the preparation of phthalic anhydrides.

It is further object of this invention to provide such a process whereby lower alkyl naphthalenes and in particular methyl naphthalenes containing sulfur may be readily converted to a sulfur-free naphthalene for conversion to phthalic anhydride, which is simple, highly effective and easy to practice.

These and other objects and advantages of this invention will become more apparent from the detailed descrip. tion set forth hereinbelow.

In accordance with the present invention, a process is provided for preparing a substantially sulfur-free naphthalene fraction, Which comprises hydrogenating a lower alkyl naphthalene-containing fraction containing sulfur in the presence of a hydrodesulfurization catalyst, and in the presence of a hydrogen-containing gas under conditions such that desulfurization is substantially complete and such that a substantial portion of the alkyl naphthalenes are hydrogenated, followed by the dehydrogenation and dealkylation of said intermediates in the presence of a dehydrogenation-dealkylation catalyst to produce a substantially sulfur-free naphthalene fraction.

By the expression alkyl naphthalenes as that and similar expressions are employed herein, it is intended to include alkyl naphthalenes having one or more alkyl substituted group containing 1 to 4 carbon atoms thereon. Thus, alkyl may be methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl or mixtures of these. These alkyl groups may be substituted at any carbon atom other than the bridge carbon atoms of the naphthalene ring structure.

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By the expression containing sulfur or sulfur-containing fraction as these and similar expressions are em ployed herein, it is meant that the lower alkyl naphthalene-containing fraction contains more than traces of sulfur, i.e., contains at least 0.10% of sulfur, though fractions containing up to about 2% of sulfur by weight are fully contemplated. This sulfur may be either free or combined in organic compounds in the fraction.

By substantially sulfur-free naphthalene and desulfur-ization substantially complete as these terms are employed herein, it is meant that the naphthalene-containing fraction should be substantially free of sulfur and should contain no'more than a maximum amount of about 0.10%.

By hydrogen containing gas as that and similar expressions are employed herein, it is meant a gaseous medium containing in excess of 50% of hydro-gen in admixture with light hydrocarbon gases, principally methane. It will be apparent that the hydrogen containing gas may be exclusively hydrogen.

In accordance with the present invention the hydrogen to hydrocarbon mole ratio fed to the reactor should be from 0.5 to 10:1.

By the expression substantial portions of the alkyl naphthalene containing fraction are hydrogenated, partly hydrogenated and similar expressions as they are employed herein, itis meant that an average hydrogenation of from 3070% of the alkyl naphthalene-containing fraction is eifected. Thus, an average of from between 30 and 70% of the theoretical hydrogen required to completely saturate the naphthalene structure is introduced thereon. Preferably, an average of from between 40 and 60% hydrogenation appears most desirable.

By alkyl naphthflene containing fraction as that and similar expressions are employed herein, it is meant fractions obtained from petroleum hydrocarbon fractions or coal tar fractions boiling within the average range of from about 375 to 600 F. and more preferably those alkyl naphthalene containing fractions boiling between 400 and 525 F. Such a fraction should contain at least 50% of alkyl naphthalenes on a Weight basis, though preferably containing at least of alkyl naphthalenes on a weight percent basis. A typical petroleum naphthalene fraction boiling in the range of 400 to 525 F. is as follows: I

The hydrogenation and desulfurization of the lower 'alkyl naphthalene-containing and, in particular, methyl naphthalene-containing fraction is carried out under a pressure of from between 400 and 1200 p.s.i., and preferably at a pressure of between 500 and 1000 psi. in a hydrogen containing gas, and in the presence of a hydro desulfurization catalyst capable of functioning both to desulfurize the alkyl naphthalenecontaining stock, as well as tofacilitate and catalyze the hydrogenation of the alkyl naphthalene component thereof.

In accordance with the'present invention, the methyl naphthalene-containing feed stock is fed over a suitable hydrodesulfurization catalyst at a WHSV (weight hourly space velocity) i.e., a ratio of the pounds of feed stock per hour to the pounds of catalyst employed. Usually, WHSV lies in the range of .10 to 10 reciprocal hours, and preferably from between 1.0 and 3 reciprocal hours. For the dehydrogenation-dealkylation step, substantially the same WHSV are employed.

The temperature employed during the hydrogenation V g and desulf-urization of the alltyl naphthalene-containing 3 fraction should be from between 600 and 900 F. and from between 700 and 800 F. is believed to be optimum.

The hydrodesulfurization catalyst may be any of a number of commercially available and known bydrodesulfurization catalysts, as for example, alumina based pellets, impregnated or otherwise, carrying as activator materials cobalt molybdate, cobalt and molybdenum oxides, nickel molybdate, nickel oxide, molybdenum oxide, nickel-tungstate, cobalt-tungstate, either alone or in combination with minor amounts of other activator materials.

For example, suitable hydrodesulfurization catalysts may contain from between 7 and 20% of molybdenum oxide, and from between 1 and 4% of cobalt oxide, the balance of the catalyst material being alumina. Catalysts within this general description have found particularly wide acceptance in the desulfurization of hydrocarbon fractions from petroleum and coal tar sources.

In the description of this invention, the illustrative hydrodesulfurization catalyst referred to is cobalt oxidemolybdenum oxide alumina based hydrodesulfurization catalyst, containing about 15% molybdenum oxide and about 3% cobalt oxide.

An important feature of this invention resides in the use of hydrodesulfurization catalysts which function to desulfurize under conditions in which the alkyl naphthalene-containing fraction is hydrogenated to a substantial degree. In conventional use. of hydrodesulfurization catalysts by the petroleum industry, hydrogenation is an undesirable side efiect in that hydrogenation reduces olefin content and converts aromatics to cyclic aliphatics', resulting in loss of gasoline octane. Thus, hydrodesulfurization conditions are usually such as to minimize these eifects by minimizing hydrogenation.

The hydrodesulfurization and hydrogenation of alkyl naphthalene fractions and specifically a methyl naphthalene sulfur containing component thereof may be illustrated by the following simple equation:

H C CH; OH:

Collialgoxida H7C\ moy enum oxidjoonAl H /C\ ass (In S containing fraction) the resulting product of desulfurization and hydrogenation being a tetrahydromethyl naphthalene, sometimes identified as a methyl tetralin. In practice, the desulfurized and hydrogenated fraction would contain a mixture of tetralins, decalins, and unconverted naphthalenes.

Operations are preferably carried out so that tetralins are the major components.

In the second important stage of this process, the partially hydrogenated desulfurized mixture is converted to a naphthalene rich fraction and hydrogen and hydrocarbon gases. This is accomplished at a temperature of between 800 and 1100 F., preferably at atmospheric pressure, although pressures up to several hundred pounds may be employed. Even partial vacuum may be employed, if desired.

- The dehydrogenation-dealkylation is preferably accomplished by passing a hydrogenated-desulfurized mixture under these conditions over a suitable catalyst, as for example, activated carbon, since it results in minimum degradative cracking results. The carbon may be activated by the use of steam or inert gases at elevated temperatures, and may be derived from a variety of sources, including petroleum sources, bituminous coal, or other sources known to those skilled in the art. The catalyst may be finely divided or pelleted and should have a high surface area and a low content of volatile matter. Inorganic materials may be, and frequently are, present,

(In S free fraction) In order to illustrate the present invention, the following examples are given primarily by way of illustration. No details are to be construed as limiting the present invention, except as they appear in the appended claims. All parts and percentages are by weight unless otherwise specifically designated.

Active carbon Example 1 A methyl naphthalene-containing fraction, containing essentially a mixture of l-methyl naphthalene and 2- methyl naphthalene and about 1% by weight of sulfur, was passed over a cobalt oxide-molybdenum oxidealumina based pelleted desulfurization catalyst in a hydrogen atmosphere, at temperatures of 705 F., a pressure of 750 p.s.i., WHSV of 1.8, and a hydrogen to hydrocarbon ratio of 5:1.

A hydrogenated-desulfurized methyl naphthalene-containing fraction analyzing as 5% of low boilers, 27% of methyl decalin, 44%. of methyl tetralin and 24% of methyl naphthalene and containing less than 0.05% sulfur resulted. This intermediate production was thereafter passed over a suitable dealkylation-dehydrogenation catalyst, in this case, x 4; activated carbon pellets, at a temperature of between 900 and 1000 F. at atmosphereic pressure, and at a WHSV of 1.5 and thereafter to a suitable products collection system from which naphthalene is isolated as by distillation or other suitable means.

In this connection, the naphthalene rich reaction product may be fractionally separated into a low boiler fraction, a naphthalene fraction containing a minor amount of unconverted decalins and tetralins, and an alkyl naphthalene fraction which may be recycled and mixed with fresh feed stock.

The average product composition for a 5-hour dehydnogenation-dealkylation run consisted of the following.

Component: Weight percent Gas 10 Low boilers 20 Naphthalene fraction 40 Methyl naphthalene 27 Coke 3 Materials suitable for blending in high octane gasoline consisting largely of alkyl benzenes.

Example 2 A feed stock boiling in the range of 400 to 525 C., consisting of 20% naphthalene, 28% l-methylnaphthalene, 41.5% Z-methyl naphthalene, and 10% poly-alkylnaphthalenes and .5 sulfur was passed over a cobalt oxidemoly bdenum oxide-alumina based pelleted catalyst in a hydrogen atmosphere, at a temperature of 700 F, a pressure of 750 p.s.i., a WHSV of 2, and a hydrogen to hydrocarbon ratio of 4:1. This stock was hydrogenated to 45% of theory and tdesulfurized to less than 0.05% sulfur.

This hydrogenated-desulfurized intermediate was then passed over a suitable idealkylation-dehydrogenation catalyst at a temperature of 1025 F. at atmospheric pressure and at a WHSV of 1.0, and thereafter to a suitable product collection system from which naphthalene was isolated by distillation in accordance with the pro cedure desired above in Example 1.

The average product composition for a 3-hour dehydrogenation-dealkylation run consisted of the following.

Materials suitable for blending in high octane gasoline, consisting largely of alkyl benzenes.

The sulfur free naphthalene fractiousmay be oxidized to phthalic anhydride in accordance with known fluid bed oxidation procedures such as for example those described in US. Patent No. 2,783,249. Yields of 90 to 100 pounds of phthalic anhydride per 100 pounds of naphthalene inaction are obtained. As noted hereinaibove, the removal of sulfur from naphthalene stock is essential for efiicient extended runs, because of the poisoning eiiect of sulfur on catalyst employed in the conversion. of naphthalene to phthalie anhydride. A standard vanadium oxide silicapyrosulfate type (V O SiO K S2Oq), Such as that described in detail in US. Patent No. 2,698,330, is an example of a suitable oxidation catalyst readily poisoned by sulfur. Such catalysts usually comprise from about 40 to 75% by weight of a calcined gel of silica, impregnated substantially uniformly with from about 20 to 50% and preferably from about 46 to about 47% of potassium sulfate, calculated as potassium sulfate, and based on the calcined weight of the catalyst from about 3 to: 25% and preferably from about 8 to 15% of vanadium pentoxide in the finished catalyst. Oxides of cerium, iron, zirconium, molybdenum or silver, or mixture thereof, may be included as promoters in amounts ranging from about 0.05% to about 5% and preferably from'about .02 to about 2% by weight. Details of this poisoning efiect in fluid bed procedures are developed more fully in copending application Serial No. 563,887, filed February 7, 1956, now US. Patent No. 2,989,544.

We claim:

1. A process for preparing a substantially sulfur-free naphthalene suitable for ready conversion to phthalic anhydride, which comprises hydrogenating and hydrodesulfurizing an alkyl naphthalene containing fraction containing at least 0.10% sulfur, in the presence of a hydrogen containing gas and in the presence of a hydrodesulfurization catalyst capable of functioning both to catalyze the hydrogenation and desulfurizati-on and to form an intermediate sulfur-free partially hydrogenated alkyl naphthalene containing fraction and thereafter de hydrogenating and dealkylating said fraction in the presence of a dehydrogenation-dealkylation catalyst whereby a substantially sulfur-free naphthalene is obtained.

2. A process according to claim 1 in which the alkyl naphthalene containing fraction is a methyl naphthalene containing fraction. 1

, 3. A process according to claim 1 in which hydrogenation and desulfurization is carriedout at a temperature from between 700 and 800 F., at a pressure of from between 500 and 1000 psi, and at a WHSV of 0.10 to 10.0.

4. A process according to claim 1 in which the dealkylation and dehydrogenation is carried out at a temperature of 800 to 1100 F. and at a WHSV of 0.10 and 10.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR PREPARING A SUBSTANTIALLY SULFUR-FREE NAPHTHALENE SUITABLE FOR READY CONVERSION TO PHTHALIC ANHYDRIDE, WHICH COMPRISES HYDROGENATING AND HYDRODESULFURIZING AN ALKYL NAPHTHALENE CONTAINING FRACTION CONTAINING AT LEAST 0.10% SULFUR, IN THE PRESENCE OF A HYDROGEN CONTAINING GAS AND IN THE PRESENCE OF A DESULFURIZATION CATALYST CAPABLE OF FUNCTIONING BOTH TO CATALYZE THE HYDROGENATION AND DESULFURIZATION AND TO FORM AN INTERMEDIATE SUFLUR-FREE PARTIALLY HYDROGENATED ALKYL NAPHTHALENE CONTAINING FRACTION AND THEAFTER DEHYDROGENATING AND DEALKYLATING SAID FRACTION IN THE PRESENCE OF A DEHYDROGENATION-DEALKYLATION CATALYST WHEREBY A SUBSTANTIALLY SULFUR-FREE NAPHTHALENE IS OBTAINED. 